FIG. 1a illustrates a communication system 10 including a light source 12 driving a light modulator 14, which receives data or information at an input port 16. Modulator 14 modulates the light from source 12 in known manner to produce modulated light at an output port 14o. The modulated light is applied to a first input port 18i1 of an amplifying light fiber illustrated as a block 18. Amplifying light fiber 18 receives pump energy at a second input port 18i2. In response to the applied modulated light and the pump energy, amplifying light fiber 18 produces amplified modulated light at an output port 18o. This amplified modulated light may be processed in any manner, and may be transmitted by way of a conventional nonamplifying fiber to a remote location. Ultimately, the amplified modulated light is applied to a light-to-electric converter, such as a detector (DET) illustrated as a block 20, to produce an electrical signal representative of the information originally modulated onto the light beam.
Those skilled in the art know that amplifying light fibers may be in the form of doped optical fibers, and that the gain per unit length of such amplifying optical fibers is relatively low. In order to obtain sufficient amplification for various purposes, the lengths of amplifying optical fiber must be relatively long. The lengths of optical fiber may be long enough so that it is convenient to wind the fiber around a mandrel, such as around a right circularly cylindrical mandrel.
Those skilled in the art also know that the amplification of signal is always attended by unwanted noise, and that it is desirable to reduce the noise whenever possible. The noise associated with the amplifying optical fiber 18 of FIG. 1a includes shot noise, which tends to be random.
FIG. 1b is a simplified perspective or isometric view of a portion of an amplifying light fiber which may be used in the arrangement of FIG. 1a. In FIG. 1b, the amplifying optical fiber is designated 18f, and the fiber 18f is surrounded by a cladding 18c. The amplifying optical fiber may as known be doped with erbium (Er), or with any other matter to achieve gain.
Improved light amplification arrangements are desired.